Influence of adjunct use andcheese microenvironment on nonstarter lactic acid bacteria populations in Cheddar-type cheese

This study investigated population dynamics of starter, adjunct, and nonstarter lactic acid bacteria (NSLAB) in reduced-fat Cheddar and Colby cheese made with or without a Lactobacillus casei adjunct. Duplicate vats of cheese were manufactured and ripened at 7°C. Bacterial populations were monitored periodically by plate counts and by DNA fingerprinting of cheese isolates with the random amplified polymorphic DNA technique. Isolates that displayed a unique DNA fingerprint were identified to the species level by partial nucleotide sequence analysis of the 16S rRNA gene. Nonstarter biota in both cheese types changed over time, but populations in the Colby cheese showed a greater degree of species heterogeneity. The addition of the L. casei adjunct to cheese milk at 104 cfu/ml did not completely suppress “wild” NSLAB populations, but it did appear to reduce nonstarter species and strain diversity in Colby and young Cheddar cheese. Nonetheless, nonstarter populations in all 6-mo-old cheeses were dominated by wild L. casei. Interestingly, the dominant strains of L. casei in each 6-mo-old cheese appeared to be affected more by adjunct treatment and not cheese variety

Reaction Networks For Interstellar Chemical Modelling: Improvements and Challenges

We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes -- ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination -- is reviewed. Emphasis is placed on those reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalysed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase.Comment: Accepted for publication in Space Science Review

Genetic and Physiological Responses of \u3ci\u3eBifidobacterium animalis\u3c/i\u3e subsp. \u3ci\u3elactis\u3c/i\u3e to Hydrogen Peroxide Stress

Consumer interest in probiotic bifidobacteria is increasing, but industry efforts to secure high cell viability in foods is determined by these anaerobes’ sensitivity to oxidative stress. To address this limitation, we investigated genetic and physiological responses of two fully sequenced Bifidobacterium animalis subsp. lactis strains, BL-04 and DSM 10140, to hydrogen peroxide (H2O2) stress. Although the genome sequences for these strains are highly clonal, prior work showed they differ in both intrinsic and inducible H2O2 resistance. Transcriptome analysis of early stationary phase cells exposed to a sub-lethal H2O2 concentration detected significant (P2O2 stress resistance might be due to a mutation in a BL-04 gene encoding long chain fatty acid-coA ligase. To explore this possibility, membrane fatty acids were isolated and analyzed by GC-MS. Results confirmed the strains had significantly different lipid profiles; the BL-04 membrane contained higher percentages of C14:0 and C16:0, and lower percentages of C16:1n7 and C18:1n9. Alteration of the DSM 10140 membrane lipid composition using modified growth medium to more closely mimic that of BL-04 yielded cells that showed increased intrinsic resistance to lethal H2O2 challenge, but did not display an inducible H2O2 stress response. Results show deliberate stress induction or membrane lipid modification can be employed to significantly improve H2O2 resistance in B. animalis subsp. lactis strains

Laboratory experiments on interstellar ice analogs: The sticking and desorption of small physisorbed molecules

Molecular oxygen and nitrogen are difficult to observe since they are infrared inactive and radio quiet. The low O2 abundances found so far combined with general considerations of dense cloud conditions suggest molecular oxygen is frozen out at low temperatures (< 20 K) in the shielded inner regions of cloud cores. In solid form O2 and N2 can only be observed as adjuncts within other ice constituents, like CO. In this work we focus on fundamental properties of N2 and O2 in CO ice-gas systems, e.g. desorption characteristics and sticking probabilities at low temperatures for different ice morphologies

The c2d Spitzer Spectroscopic Survey Of Ices Around Low-Mass Young Stellar Objects. I. H2O And The 5-8 Mu M Bands

To study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low-luminosity YSOs (L similar to 0.1-10 L-circle dot) using 3-38 mu m Spitzer and ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well-studied massive YSOs (L similar to 10(5) L-circle dot). The long-known 6.0 and 6.85 mu m bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. The 6.0 mu m band is often deeper than expected from the bending mode of pure solid H2O. The additional 5-7 mu m absorption consists of five independent components, which, by comparison to laboratory studies, must be from at least eight different carriers. Much of this absorption is due to simple species likely formed by grain surface chemistry, at abundances of 1%-30% for CH3OH, 3%-8% for NH3, 1%-5% for HCOOH, similar to 6% for H2CO, and similar to 0.3% for HCOO- relative to solid H2O. The 6.85 mu m band has one or two carriers, of which one may be less volatile than H2O. Its carrier(s) formed early in the molecular cloud evolution and do not survive in the diffuse ISM. If an NH4+- containing salt is the carrier, its abundance relative to solid H2O is similar to 7%, demonstrating the efficiency of low-temperature acid-base chemistry or cosmic-ray-induced reactions. Possible origins are discussed for enigmatic, very broad absorption between 5 and 8 mu m. Finally, the same ices are observed toward massive and low-mass YSOs, indicating that processing by internal UV radiation fields is a minor factor in their early chemical evolution.NWO SpinozaNOVAEuropean Research Training Network PLANETS HPRN-CT-2002-00308NASA Origins NAG5-13050NASA Hubble Fellowship 01201.01NASA NAS 5-26555Astronom

Spatially resolved l-CH3+ emission in the Horsehead PDR: on the need for a top-down hydrocarbon chemistry

Small hydrocarbons, such as C2H, C3H and C3H2 are more abundant in photo-dissociation regions (PDRs) than expected based on gas-phase chemical models. To explore the hydrocarbon chemistry further, we observed a key intermediate species, the hydrocarbon ion l-C3H+, in the Horsehead PDR with the Plateau de Bure Interferometer at high-angular resolution (6''). We compare with previous observations of C2H and c-C3H2 at similar angular resolution and new gas-phase chemical model predictions to constrain the dominant formation mechanisms of small hydrocarbons in low-UV flux PDRs. We find that, at the peak of the HCO emission (PDR position), the measured l-C3H+, C2H and c-C3H2 abundances are consistent with current gas-phase model predictions. However, in the first PDR layers, at the 7.7 mum PAH band emission peak, which are more exposed to the radiation field and where the density is lower, the C2H and c-C3H2 abundances are underestimated by an order of magnitude. At this position, the l-C3H+ abundance is also underpredicted by the model but only by a factor of a few. In addition, contrary to the model predictions, l-C3H+ peaks further out in the PDR than the other hydrocarbons, C2H and c-C3H2. This cannot be explained by an excitation effect. Current gas-phase photochemical models thus cannot explain the observed abundances of hydrocarbons, in particular in the first PDR layers. Our observations are consistent with a top-down hydrocarbon chemistry, in which large polyatomic molecules or small carbonaceous grains are photo-destroyed into smaller hydrocarbon molecules/precursors.Astronom

Comparison of the complete genome sequencesof Bifidobacterium animalis subsp. lactis DSM 10140 and Bl-04

Bifidobacteria are important members of the human gut flora, especially in infants. Comparative genomic analysis of two Bifidobacterium animalis subsp. lactis strains revealed evolution by internal deletion of consecutive spacer-repeat units within a novel clustered regularly interspaced short palindromic repeat locus, which represented the largest differential content between the two genomes. Additionally, 47 single nucleotide polymorphisms were identified, consisting primarily of nonsynonymous mutations, indicating positive selection and/or recent divergence. A particular nonsynonymous mutation in a putative glucose transporter was linked to a negative phenotypic effect on the ability of the variant to catabolize glucose, consistent with a modification in the predicted protein transmembrane topology. Comparative genome sequence analysis of three Bifidobacterium species provided a core genome set of 1,117 orthologs complemented by a pan-genome of 2,445 genes. The genome sequences of the intestinal bacterium B. animalis subsp. lactis provide insights into rapid genome evolution and the genetic basis for adaptation to the human gut environment, notably with regard to catabolism of dietary carbohydrates, resistance to bile and acid, and interaction with the intestinal epithelium. The high degree of genome conservation observed between the two strains in terms of size, organization, and sequence is indicative of a genomically monomorphic subspecies and explains the inability to differentiate the strains by standard techniques such as pulsed-field gel electrophoresis